1. Field of the Invention
This invention relates to a semiconductor device and a method of fabrication thereof, as well as a circuit board and electronic equipment.
2. Description of Related Art
Methods are known of forming a bump on an electrode of a semiconductor chip, using wire bonding techniques. Japanese Patent Application Laid-Open No. 57-163919, for example, discloses a method of creating a bump by using a capillary tube to bond a wire to an electrode, then forming a bump by tearing off the wire so that a fragment of the wire remains on the electrode. This method makes it possible to form a bump rapidly, in comparison with the method in which plating is accumulated.
However, it is not possible to guarantee that a bump formed by tearing off a wire has a sufficiently flat upper surface. This causes no problems when semiconductor chip are bonded face-down to a substrate, but it does cause problems in that connection accuracy deteriorates when a lead is bonded to the bump. In other words, an upper surface of the bump is jagged or has very little surface area that is flat, and thus insufficient surface area thereof is in contact with the lead and thus the lead may separate from the bump.
This invention was devised to solve the above problem and has as an objective thereof the provision of a semiconductor device having a bump which can be formed easily and which can also be connected in a suitable manner to a lead, a method of fabricating such a semiconductor device, a circuit board, and electronic equipment.
(1) According to a first aspect of the present invention, there is provided a method of fabricating a semiconductor device, comprising:
a first step of bonding a conductive wire to any one of a plurality of electrodes of a semiconductor chip;
a second step of tearing off the bonded conductive wire in such a manner that a part of the conductive wire remains on the one of the electrodes;
a third step of pressing the part of the conductive wire that remains on the one of the electrodes, to form a bump comprising a base portion in contact with the one of the electrodes and a head portion of a width that is less than the width of the base portion; and
a fourth step of bonding the bump and a lead;
wherein a distance D between an upper surface of the base portion of the bump and an upper surface of the head portion of the bump is set in the third step in such a manner that: 0 less than Dxe2x89xa66 xcexcm.
With this aspect of the invention, a bump can be formed simply by bonding a conductive wire to an electrode, tearing off it to leave a part thereof on the electrode, and then pressing and deforming that part. These steps take less time in comparison with the steps required for forming the bump by plating. In addition, the distance D between the upper surface of the base portion of the bump and the upper surface of the head portion thereof is set to be such that: 0 less than Dxe2x89xa66 xcexcm. In this case, the condition that D is not equal to zero means that it is not necessary to press the remaining part of the conductive wire on the electrode so strongly that the head portion disappears. This means that the shock imparted to the semiconductor chip when the remaining part of the conductive wire is pressed can be reduced. The condition that D is less than or equal to 6 xcexcm means that the quality of the bonding of a lead can be kept constant, regardless of the width of the head portion of the bump. This enables connection of the lead with a good positional accuracy.
(2) In this method of fabricating a semiconductor device, a width A of the base portion of the bump, a width B of the head portion of the bump, and a width C of the lead may be in a relationship such that: C greater than (Axe2x88x92B)/2.
(3) In this method of fabricating a semiconductor device, the first and second steps may be repeated before the third step, to provide parts of conductive wires on the plurality of electrodes; and the parts of the conductive wires remaining on the plurality of electrodes may be simultaneously pressed in the third step, to form a plurality of bumps simultaneously.
Since a plurality of bumps are simultaneously formed, the process can be shortened.
(4) In this method of fabricating a semiconductor device, the lead may protrude into an opening formed in a substrate; and the bump may be disposed within the opening such that the lead is bonded to the bump within the opening in the fourth step.
(5) In this method of fabricating a semiconductor device, the lead may be formed on a substrate; and the bump may be arranged to face the lead on the substrate for the face-down bonding of the semiconductor chip in the fourth step.
(6) In this method of fabricating a semiconductor device, the bump may be bonded to the lead in the fourth step by an anisotropic conductive material formed of conductive particles dispersed within an adhesive.
(7) According to a second aspect of the present invention, there is provided a semiconductor device comprising:
a semiconductor chip having a plurality of electrodes;
a bump which is formed on each of the electrodes and has a base portion in contact with one of the electrodes and a head portion of a width smaller than the width of the base portion;
a lead bonded to the bump; and
a substrate on which the lead is formed;
wherein a distance D between an upper surface of the base portion of the bump and an upper surface of the head portion of the bump is such that: 0 less than Dxe2x89xa66 xcexcm.
With this aspect of the invention, the lead is bonded to a head portion that has a width less than that of a base portion of the bump. In this case, the condition that D is less than or equal to 6 xcexcm means that the quality of the bonding of a lead can be kept constant, regardless of the width of the head portion of the bump. This enables connection of the lead with a good positional accuracy.
(8) In this semiconductor device, a width A of the base portion of the bump, a width B of the head portion of the bump, and a width C of the lead may be in a relationship such that: C greater than (Axe2x88x92B)/2.
(9) In this semiconductor device, the substrate may have an opening, the lead may protrude into the opening in the substrate, and the bump may be bonded to the lead within the opening.
(10) In this semiconductor device, the lead may be formed on a substrate, and the bump may be arranged to face the lead on the substrate for the face-down bonding of the semiconductor chip.
(11) In this semiconductor device, the bump may be bonded to the lead by an anisotropic conductive material formed of conductive particles dispersed within an adhesive.
(12) According to a third aspect of the present invention, there is provided a circuit board on which is mounted the above described semiconductor device.
(13) According to a fourth aspect of the present invention, there is provided electronic equipment having the above described semiconductor device.